Research by US Geological Survey scientists has demonstrated that the virtual absence of mayflies, stoneflies, and caddisflies from the Colorado River in Grand Canyon was partly due to acute mortality of aquatic insect eggs arising from hydropower generation at Glen Canyon Dam. In the summer of 2018 and 2019, dam management practices were experimentally modified in an attempt to increase the production and diversity of aquatic insects in the Colorado River in Grand Canyon (Arizona, USA). These experimental “Bug Flows” involved hourly flow fluctuations for hydropower generation during weekdays, coupled with steady, low flows on weekends to reduce aquatic insect egg desiccation and mortality. To track ecosystem response to this flow experiment, samples of emergent insects were collected from throughout the 400-kilometer-long Grand Canyon segment using light traps deployed almost entirely by citizen scientists. This citizen science light trapping has occurred since 2012, providing six years of baseline data (2012-2017) and two years of experimental data (2018 & 2019). A 400% increase in the abundance of caddisflies in 2018 relative to the baseline suggested Bug Flows were an effective mitigation strategy, but caddisfly abundance in 2019 declined back to the baseline value. However, data interpretation is complicated by a large increase in suspended sediment loading during winter and spring of 2019 relative to 2018. Bug Flow experimentation is also occurring in 2020 and may help determine whether this mitigation strategy is effective at increasing the abundance and diversity of aquatic insect populations in Grand Canyon.
Presented by Ted Kennedy, USGS
Photo Credit: USGS and Freshwaters Illustrated
This lecture is part of the Colorado River Days Flagstaff 2020 festival. For more information visit http://www.coloradoriverdaysflagstaff.org/